The structure of a reading and writing horizontal head for longitudinal recording is shown on FIG. 1. Various films (whose relative dimensions have not been observed in order to provide more clarity) are deposited and engraved in a semiconductive substrate 10 so as to form a magnetic circuit 12 with an airgap filled up by a nonmagnetic spacer 14 and a conductive winding 16. This winding 16 includes two sets of windings interconnected by a link 18; each set is wound around one magnetic pillar 20, 21. These magnetic pillars 20, 21 connect the first and second horizontal polar pieces 22, 23 of the circuit 12.
The winding 16 is connected at its two extremities by means of links 24, 26 traversing the substrate 10 to contact blocks 28, 30 disposed on the lower face of the substrate.
The track to be written and/or read 32 runs off above the airgap.
Various embodiments of such heads are described in the European patents EP-A-152 326 and EP-A-262 028.
Compared with this known thin film technology, another technique has been developed using the characteristics of materials with the Hall effect. Such materials make it possible to embody reading heads for extremely narrow recording tracks.
The document FR 2 518 792 describes a vertical magnetic head using a Hall effect sensor. Such a magnetic head is diagrammatically shown on FIG. 2. As can be observed on this figure, the Hall effect sensor 34 is disposed in a space situated between two polar pieces 36, 38. These polar pieces 36, 38 are placed vertically with respect to the magnetic recording medium 32 and are separated at the level of the section of the head close to the medium by a nonmagnetic spacer 40.
Such a magnetic head only comprises a single Hall effect sensor; it is thus subjected to thermal or electronic drifts, these drifts needing to be made up for.
FIG. 3 diagrammatically represents another known vertical magnetic head and comprising a Hall effect sensor. This magnetic head is described in detail in the document U.S. Pat. No. 3,800,193.
The polar pieces 36, 38 join up at each of their extremities. They are firstly separated by a nonmagnetic spacer 40 at the section of the polar pieces opposite the magnetic recording medium 32, and secondly by the Hall effect sensor 34.
This magnetic head exhibits the same drawbacks as the previous one.